1. Field of the Invention
The present invention generally relates to the design of hulls for watercraft and, more particularly, to hull structures of vessels allowing docking together or joint functioning of vessels.
2. Description of the Prior Art
Waterborne vessels have been used since ancient times and for many purposes and particularly for the transport of large objects or heavy cargoes. The need for vessels to perform in a variety of water and weather conditions and the various purposes for which such vessels have been intended has led to a great variety of hull designs. In particular, the often conflicting desire to increase both the speed and operational range of vessels has led to the development of hydrofoil designs.
Hydrofoils function to increase speed by decreasing the wetted area of hulls by producing lift sufficient to support the main hull of a vessel above the water and, in general, have been relatively successful for passenger service and the transporting of relatively light loads. However, the need to generate sufficient lift to entirely replace displacement as a means for supporting the vessel requires relatively high speeds which increases fuel consumption and reduces the range of the vessel. Fuel efficiency of such vessels was often compromised since the propulsion arrangement must serve both hull-borne and foil-borne modes of operation and thus cannot be optimized for either. This has led to dual propulsion systems for each of the hull borne and foil borne modes of operation. However, dual propulsion systems are not fully optimize efficiency since the necessarily involve additional weight. Further, the structure required to produce such lift increases with the displacement of the vessel and the size of vessels to which hydrofoils can be applied has, as a practical matter, been relatively limited.
As an alternative for the purpose of extending the potential of hydrofoils to larger vessels, the so-called hybrid hydrofoil concept has drawn substantial interest in recent years. This type of design uses one or more submerged hulls or pods connected to the vessel by one or more struts as a structural base upon which hydrofoils can be mounted. The pod can be used to carry fuel and/or motive power systems and preferably provide some positive static buoyancy for the vessel. By providing a significant amount of support for the vessel by the static buoyancy of the pod, the hydrofoils are thus required to provide less dynamic lift, often only on the order of 30%-70% of the displacement of the entire vessel. The provision of podded propulsion through the submerged hull is advantageous since the podded hull will always be submerged.
A particular design for a hybrid hydrofoil configuration has included a single pod with counter-rotating propellers (possibly co-axial) connected to the displacement hull of the vessel by a single narrow strut running a substantial portion of the length of the vessel. Other designs include a single propeller on the stern of the pod. Two pair of foils, each equipped with flaps for producing lift and dynamic stabilization of the vessel are provided near the fore and aft ends of the pod. Unflapped foils using incidence control can also be applied. By the combination of providing a portion of the vessel support through the static buoyancy of the pod and strut and merely using the foils to lift the displacement hull from the water, reducing wetted area of the combination hull of the vessel, the latitude of operating conditions has been increased while efficiency and range have been increased while the speed of hydrofoil designs has been maintained. Additionally, it should be understood that even if the entire pod is filled with fuel, such fuel is typically less dense than water and substantial static buoyancy can be obtained essentially from additional fuel-carrying capacity in the hybrid hydrofoil design. Further, since less than the total vessel weight must be provided as dynamic lift from the hydrofoils, the hybrid hydrofoil concept can be applied to vessels of greater displacement than conventional hydrofoil designs.
Also, in recent years, many vessels of extremely large size have been built for particular purposes, such as Aircraft carriers. Another type of large vessel is the so-called Carrier of Large Objects (CLO) which typically includes a wet-well to allow a large object, such as a barge, to be carried into the wet well while afloat. The CLO thus can provide increased efficiency of transportation of the object by enclosing the floating object in a more efficient hull shape. The CLO can also serve to transport smaller vessels of limited range such as air cushion vehicles and surface effect ships. However, the size of a CLO limits its top speed and maneuverability. Further, the wet well can be drained to more completely support the object or allow repair and servicing thereof. Thus a CLO can provide a facility for refueling or refitting of smaller vessels at sea and while under way.
However, the dimensions of the wet well of a CLO are, of course, limited and cannot generally accommodate the overall height of a relatively large hybrid hydrofoil hull vessel in the hullborne mode of support. Further, the hydrofoil structure protruding from the submersible hull would be subject to damage even if the hybrid hydrofoil hull could be accommodated inside the CLO. Support for the entire hybrid hydrofoil vessel would also be difficult and might preclude draining of the CLO wet well during transport thereof.